Historically asbestos has been used in asphalt roofing compositions and other organic coating materials for roofing applications, automotive underbody coatings, foundation coatings, mastics and adhesives, and other specialty applications to provide a thixotropic structure that is sag resistant and does not settle in storage. Environmental concerns about asbestos have constrained the industry to seek alternative gelling and viscosifying agents. Clay minerals and particularly attapulgite clay minerals have been shown to be effective and are widely used. The attapulgite clays require the use of cationic surfactants to fully develop the gelling and viscosity properties of the clay. Cationic surfactants which have been used in this application include quaternary ammonium salts such as dicocodimethyl ammonium chloride, tallow trimethyl ammonium chloride, and methyl-1-oleylamidoethyl-2-oleylimidazolinium methyl sulfate. Also used are alkyloxyalkylamine salts such as isodecyloxypropyl ammonium acetate. Our copending application Ser. No. 08/482,483, now U.S. Pat. No. 5,529,621, incorporated herein by reference, discloses surfactants which are organic salts of surface active polyamines and carboxylic acids, wherein the polyamines have the structure: ##STR1## wherein R is chosen from the group consisting of (i) alkyl or alkenyl containing from about 10 to about 22 carbon atoms, and (ii) R'--O--CH2CH2CH2-- wherein R' is alkyl containing from about 8 to about 22 carbon atoms, A is a divalent hydrocarbyl group containing about 2 to about 6 carbon atoms, and n is an integer from about 1 to about 3; and the carboxylic acids have the structure:
R"--COOH PA1 an organic adhesive material, usually an asphalt cutback, PA1 a clay mineral or mixture of clay minerals, PA1 at least one cationic surfactant, and PA1 at least one acid with a pK.sub.A value less than about 5; PA1 an organic adhesive material, usually asphalt cutback, PA1 a clay mineral, or a mixture of clay minerals, PA1 a cationic surfactant or a mixture of cationic surfactants, and PA1 an acid with a pK.sub.A value less than about 5, or a mixture of such acids; PA1 R"--COOH PA1 1. providing a quantity of organic binding or adhesive material, which is preferably an asphalt cutback, PA1 2. adding a cationic surfactant and mixing, PA1 3. adding a clay mineral and mixing, PA1 4. optionally adding an additional quantity of organic adhesive material and mixing, PA1 5. adding an acid with a pK.sub.A value less than about 5, and mixing.
wherein R" is alkyl or alkenyl containing about 6 to about 28 carbon atoms.
To produce asphalt compositions with a gelled consistency for cements or mastics historically requires clay contents of 12 percent by weight or more. For clays to provide the desired thixotropy they must contain about 10 percent by weight water. To meet the requirements of ASTM D-4586, "Standard Specification for Asphalt Roof Cement, Asbestos Free", the final composition must contain less than 3 percent water, and for the maximum moisture insensitivity of the asphalt composition, preferably contains less than 1 percent water. The use of high levels of clay, however, may cause the resulting asphalt composition to contain an undesirable level of water which renders the applied coating moisture sensitive, i.e. susceptible to softening, disintegration, loss of adhesion, or other damaging effects when exposed to environmental moisture. Furthermore, the clay minerals used are hydrophilic independent of their water content, and also contribute to the moisture sensitivity of the asphalt composition.
Clays that are desirable as viscosifying or gelling agents have a small uniform particle size and a large surface area. These clays are more costly than the other components in the asphalt composition, so their use at higher levels increases the cost of the compositions on a weight basis. Further, the clays are more dense than the other components, so their use at higher levels increases the density of the final asphalt composition. Since the final compositions are typically sold by volume rather than by weight, and the clay component is typically sold by weight, the cost of the clay is usually not recovered. The surfactants also are costly components of the asphalt compositions, and reduction in the level of their use also significantly reduces the cost of the asphalt formulation. An economic advantage results if the quality of the final product can be maintained at reduced levels of clay and surfactant.
Thickened asphalt compositions frequently contact metal surfaces in their application as roofing and other construction materials and underbody coatings. It is desirable to protect these metal surfaces from corrosion by the inclusion of a corrosion inhibiting material in the asphalt compositions.